1. Field of the Invention
The present invention relates to a quantum cascade laser.
2. Description of the Related Art
Quantum cascade lasers (QCLs) are known as semiconductor optical devices which emit infrared light at an emission wavelength of 2 to 10 μm. Quantum cascade lasers are small-sized, low-cost light sources that can be used in the fields of environmental gas analysis, medical application, industrial processing, and the like. As the current-confinement structure of quantum cascade lasers, for example, a ridge-type waveguide structure described in Non-Patent Document 1 (Applied Physics Letters, vol. 72, pp. 3130-3132, 1998) is known, in which the ridge-type waveguide structure is referred to as a “shallow etched ridge waveguide laser”.